Corona discharge device with means to heat the discharge electrodes to increase the discharge current

ABSTRACT

In a corona discharge device utilized in electrophotography, means to heat directly or indirectly the corona discharge electrode is provided to increase corona discharge current.

Unite States Patent [72] Inventor Seiichi Miyakawa Nagareyamashi, Japan [21] Appl. No. 836,024 [22] Filed June 24, 1969 [45] Patented Nov. 16, 1971 [73] Assignee Katsuragawa Denki Kabushiki Kaisha Tokyo-to, Japan [54] CORONA DISCHARGE DEVICE WITH MEANS T0 HEAT THE DISCHARGE ELECTRODES TO INCREASE THE DISCHARGE CURRENT 4 Claims, 3 Drawing Figs.

[52] US. Cl 250/495 [51] Int. Cl 603g 15/00 HEATING CURRENT SOURCE [50] Field of Search ..250/49.561, 49.560, 49.562; 317/262 A; 204/328, 323

[56] References Cited UNITED STATES PATENTS 2,740,] 84 4/1956 Thomas 250/495 2,965,481 12/1960 Gundlach 250/495 Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney-Bosworth, Sessions, Herrstrom & Cain ABSTRACT: In a corona discharge device utilized in electrophotography, means to heat directly or indirectly the corona discharge electrode is provided to increase corona discharge current.

VOLTAGE (SOURCE PATENTEUNUV 16 I97! VOLTAG E (SOURCE SOURCE HEATING L CURRENT SOURCE HEATING CURRENT SOURCE CORONA DISCHARGE DEVICE WITH MEANS TO HEAT 'lllhIE DISCHARGE ELECTRODES T TNCASE THE DISCHARGE CURRENT BACKGROUND OF THE INVENTION It is well known in the art to utilize a corona discharge device for depositing positive or negative electrostatic charge on the surface of a photosensitive element for use in electrophotography.

For example, in the classical electrophotography, a photosensitive element comprising a photoconductive layer and a backing electrode is used, and an electrostatic charge (usually of positive polarity) is deposited on the surface of the photoconductive layer Then, in the dark, a light image is projected upon the photosensitive layer to form an electrostatic latent image on the surface of the photosensitive layer, which is then developed in the dark.

According to a more recently developed method of electrophotography, use is made of a photosensitive element comprising a backing electrode, a photosensitivelayer having a property of trapping under electric field electric charge carriers at its trap levels to vary the dielectric constant of the layer, and a transparent highly insulative layer integrally bonded to the surface of the photosensitive layer. A latent image is formed on the surface of the highly insulative layer by the steps of depositing a charge of a predetermined polarity on the surface of the highly insulative layer and depositing a charge of the opposite polarity on the surface of the highly insulative layer concurrently with the projection of a light image thereon.

The latter method is highly advantageous because of its high resolution and high photosensitivity. Where a corona discharge device is used in the latter method, as the dielectric constant at portions of the photosensitive element corresponding to bright portions of the light image increases significantly, with the conventional corona discharge device it is impossible to reach the desired charge potential, thus limiting the intensity of the light image or while image developed therefrom. it is thought that this is caused by the insufiiciency of the density of the discharge current produced by the conventional corona discharge device. Thus, the charging capacity becomes insufficient as the sensitivity of the photosensitive element increases, thus making it impossible to increase the speed ofimage-forming operation.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved corona discharge electrode having higher discharge capacity to enable rapid deposition of the desired quantity of charge on the photosensitive element for use in electrography.

According to this invention means is provided to elevate the temperature of the corona discharge device. This can be conveniently accomplished by directly heating the fine wires comprising the corona discharge electrode or by warming the air surrounding the discharge electrode.

According to one embodiment of this invention, a cylindrical shield surrounding the corona discharge electrode in the form of a fine wire is heated by passing electric current through the shield. According to a modified embodiment of this invention, an electrically heated wire is provided adjacent the discharge electrode. In a still further embodiment, heating current is directly passed through the corona discharge electrode to heat the same.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

HO. 1 is a diagrammatic representation of a photosensitive element and a corona discharge device embodying this invention; and

FIGS. 2 and 3 are similar views of modified embodiments of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 of the accompanying drawing there is shown a photosensitive element 4 comprising a grounded backing electrode l, a photosensitive layer 2 of any photoconductive material or photosensitive material having a number of trap levels, and a transparent highly insulative layer 3 integrally bonded to the entire surface of the photosensitive layer.

Slightly above the photosensitive element 4 is disposed a corona discharge device 6 comprising a discharge electrode 9 in the form of a fine metal wire and a cylindrical shield 8 surrounding the corona discharge electrode 9, which is connected to a source of DC voltage 5. The shield E is made of an electrical resistance material and is energized by a source of supply 7.

In operation, the corona discharge device 6 is moved relative to the photosensitive element 4. Thus, where a flat photosensitive element is used, the corona discharge device is moved horizontally across the surface of the photosensitive element but where the photosensitive element is mounted on a cylinder, the cylinder is rotated. One or more of such corona discharge devices may be provided depending upon the method of forming the latent image. Light image is projected upon the photosensitive element through the corona discharge device as schematically shown by arrow A.

in one instance, the voltage of DC source 5 was maintained at a constant value of 4,800 volts. When shield 8 was heated to about 200 C. by energizing it from source 7, at a room temperature of 25 C, the corona discharge current was increased from 6 ma./cm. to 12 ma./cm. With this increased current it was possible to obtain very intense latent images and hence very clear visible images.

in the modified embodiment shown in FIG. 2, a heating wire 10 energized from a suitable source 7 is provided adjacent the corona discharge electrode 9. In this case shield 7 is grounded. The diameter of the heating wire 10 was about 0.2 mm. which is about three times as large as that of the corona discharge electrode 9. When the heating wire was heated to about 200 C., the corona discharge current was again increased to 6 ma./cm. at a room temperature of 25 C. and at a corona discharge voltage of 4,800 volts. When the temperature of heating wire 10 was increased to about 300 C., the corona discharge current was increased to 10 ma./cm.

In another embodiment shown in H6. 3, corona discharge electrode 9 is used as the heating wire too so that it is heated by current supplied from source 7. When a tungsten wire of 0.06 mm. diameter was used as the corona discharge electrode, without energizing it from source 7, corona discharge current of 6 ma./cm. was obtained at a room temperature of 25 C. and at a corona discharge voltage of 4,800 volts. When the temperature of corona discharge electrode 9 was increased to about 60 C. by the current from source 7, the corona discharge current was increased to 12 ma./cm. whereas when the temperature of the corona discharge electrode was increased to about (1., the corona discharge current was increased to 18 ma./cm.

Direct heating of the corona discharge electrode as in this embodiment of the invention results in a great increase in the charge per unit time deposited on the photosensitive element, thus enabling the provision of very clear visible images in an extremely short time which could never have been realized with the prior art corona discharge electrode.

Temperatures of less than C. can effectively increase the corona discharge current so that when the corona discharge electrode is operated at these relatively low temperatures, the operation of photosensitive elements which are inherently sensitive to the variation in ambient temperature will not be effected by the temperature of the corona discharge electrode. Moreover, linear expansion of the corona discharge electrode is negligibly small, so that heating thereof does not cause any undesirable effect upon the quality of the reproduced image.

Although the mechanism of increasing the corona discharge current caused by the increase in the operating temperature of the corona discharge electrode is not yet clearly understood, it is believed that this is caused by the decrease in the difference of work functions of the corona discharge electrode and of the surrounding air and by the increase in the mobility of electric charge around the corona discharge electrode.

In addition to the heating means illustrated in the abovedescribed embodiments of the invention, any suitable means that can increase the temperature of the corona discharge electrode or of the surrounding air may be used.

I claim:

1. A corona discharge device adapted to deposit electric charge on a photosensitive element for use in electrophotography comprising: a corona discharge generator, means for supplying energizing potential to said corona discharge generator to establish a corona discharge current, and generator heating means, independent of said corona discharge current, for heating said corona discharge generator whereby the discharge capacity of said corona discharge generator is substantially increased.

2. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a corona discharge electrode in the form of a fine wire and a cylindrical shield surrounding said corona discharge electrode, and wherein said heating means includes means for electrically heating said shield.

3. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a fine wire, and wherein said heating means includes an electric heating wire positioned relatively close to said fine wire.

4. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a corona discharge electrode in the form of a fine wire, and wherein said heating means includes means for passing heating current through said corona discharge electrode. 

1. A corona discharge device adapted to deposit electric charge on a photosensitive element for use in electrophotography comprising: a corona discharge generator, means for supplying energizing potential to said corona discharge generator to establish a corona discharge current, and generator heating means, independent of said corona discharge current, for heating said corona discharge generator whereby the discharge capacity of said corona discharge generator is substantially increased.
 2. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a corona discharge electrode in the form of a fine wire and a cylindrical shield surrounding said corona discharge electrode, and wherein said heating means includes means for electrically heating said shield.
 3. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a fine wire, and wherein said heating means includes an electric heating wire positioned relatively close to said fine wire.
 4. A corona discharge device according to claim 1 wherein said corona discharge generator comprises a corona discharge electrode in the form of a fine wire, and wherein said heating means includes means for passing heating current through said corona discharge electrode. 